Various proposals have been made of head-mounted display devices, worn on a person's head, that include a display unit and an eyepiece optical unit. An image displayed on the display unit can be observed with the eyepiece optical unit as an enlarged virtual image. Since individuals wear such head-mounted display devices, there is a desire to be able to perform eyepoint adjustment and diopter adjustment in accordance with the individual wearer's pupillary distance, head size, eyesight, and the like.
In light of such demand, for example the applicant has proposed a head-mounted display device that includes a first housing that has a display unit, a second housing that allows for adjustment of the optical path length, and a third housing that has an eyepiece optical unit. The second housing is slidable towards the front and back of the wearer with respect to the first housing, and the third housing is slidable towards the left and right of the wearer with respect to the second housing (see JP 2012-63633 A (PTL 1)). The device disclosed in PTL 1 allows for eyepoint adjustment and diopter adjustment with a simple operation by sliding the second housing towards the front and back of the wearer with respect to the first housing and sliding the third housing towards the left and right of the wearer with respect to the second housing.